General > General Technical Chat
Tape deck / turntable adjustable motors - how do they work?
Zbig:
You see those integrated brushed DC motors with a hole or two in them for speed adjustment in countless cassette tape decks or entry-to-midrange record players. If you've seen at least a couple of VWestlife's or Techmoan's YouTube videos, you know what I'm talking about. Yet I have failed to find out how do they work internally, speed regulation specifically. So, you have that hole (or two) to poke your screwdriver through and you can adjust the speed this way. But how's the speed control actually implemented? Is it just a crude, open loop speed adjustment by means of varying the voltage going to the motor from a linear regulator? Or maybe some rudimentary closed-loop control? If that's the case, how's the timebase generated (simple RC circuit? Crystal oscillator?) and speed feedback realised (optical encoder? Hall effect sensor? Other?)
PKTKS:
Vast majority K7 motors capstan drives i ve seen operate on DIRECT CONSTANT CURRENT DRIVE..
Some very vintage turntables belt drive as well and some direct driven can use optical/hall sensors with leds to speed accuracy..
Paul
NiHaoMike:
I remember taking apart a cassette player motor a long time ago and it had a centrifugal switch to regulate the speed. There was a fairly massive flywheel to smooth out the speed variation it would cause.
Benta:
@ZBig, I've absolutely no idea what you're talking about.
I've never heard of VWestlife or Techmoan before, and your description of the motors is flaky.
Please be more specific.
Zoli:
--- Quote from: PKTKS on May 28, 2022, 10:56:25 am ---Vast majority K7 motors capstan drives i ve seen operate on DIRECT CONSTANT CURRENT DRIVE..
Some very vintage turntables belt drive as well and some direct driven can use optical/hall sensors with leds to speed accuracy..
Paul
--- End quote ---
Actually, the typical cassette player motor control circuit has a limited NEGATIVE internal resistance(the current raises->the voltage raises - until the power supply allows) to compensate for the different loads(start and end of tape) to keep the rotational speed as constant as possible.
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